1 files changed, 27 insertions, 4 deletions

diff --git a/arch/x86/lib/delay_32.c b/arch/x86/lib/delay_32.c
index 4535e6d147ad..d710f2d167bb 100644
--- a/arch/x86/lib/delay_32.c
+++ b/arch/x86/lib/delay_32.c
@@ -44,13 +44,36 @@ static void delay_loop(unsigned long loops)
 static void delay_tsc(unsigned long loops)
 {
         unsigned long bclock, now;
+        int cpu;
 
-        preempt_disable();              /* TSC's are per-cpu */
+        preempt_disable();
+        cpu = smp_processor_id();
         rdtscl(bclock);
-        do {
-                rep_nop();
+        for (;;) {
                 rdtscl(now);
-        } while ((now-bclock) < loops);
+                if ((now - bclock) >= loops)
+                        break;
+
+                /* Allow RT tasks to run */
+                preempt_enable();
+                rep_nop();
+                preempt_disable();
+
+                /*
+                 * It is possible that we moved to another CPU, and
+                 * since TSC's are per-cpu we need to calculate
+                 * that. The delay must guarantee that we wait "at
+                 * least" the amount of time. Being moved to another
+                 * CPU could make the wait longer but we just need to
+                 * make sure we waited long enough. Rebalance the
+                 * counter for this CPU.
+                 */
+                if (unlikely(cpu != smp_processor_id())) {
+                        loops -= (now - bclock);
+                        cpu = smp_processor_id();
+                        rdtscl(bclock);
+                }
+        }
         preempt_enable();
 }